Introduced: 1984 (white box / single motor version), 1995 (Plus / Spectrum version), 2009 (Blue Label / DCC version) and 2014 (DCC-Sound version)
As is Bachmann's wont, there have been several radically different versions of this model. The first version has a somewhat minimalistic all-metal / split-frame chassis. The motor is a skew-wound 3-poler. All-wheels provide pickup, but only the forward truck is geared. All gearing is plastic. Two of the wheels are equipped with traction tires. The motor is actually attached to the forward truck assembly, and if you were to remove the whole shebang from the chassis, you could actually run it down the track all by itself. The couplers are truck-mounted Rapidos, The wheel flanges on this first version (along with all subsequent versions) are reasonably sized, so no problems on Code-55 track. And starting right with this first release, all versions have a decidedly toyish looking blinky LED lurking atop the cab. Directional lighting is also provided. Unfortunately, the headlight actually lights up the entire cab and is, as a consequence, also decidedly toyish looking. All of the fancy lighting is actually built right into the shell (on both early versions).
Performance is not great. It's pretty loud and not particuarly smooth. More annoyingly, the rear truck was built without any fore/aft play. Consequently, it has just one heck of a time keeping its wheels on the rails - basically derailing whenever faced with any sort of unevenness in the track. The minimilistic chassis probably doesn't help much in that regard either. Looks-wise, this model has its problems. The shell is way too wide, the detailing is somewhat coarse and the paint is nothing to write home about. Interestingly enough, this is the only version with the correct see-right-through-to-other-side center "porch".
Circa 1995, Bachmann re-released this model under their "Plus" label with a completely redesigned mechanism. This same model was repackaged under Bachmann's "Spectrum" label starting circa 1998 -
This second version has an enormous split-frame chassis with two 5-pole / skew-wound motors - one for each truck. Each motor is equipped with a single flywheel. All wheels are geared and provide pickup (no traction tires). Current is ferried from the wheels to the chassis halves via oval metal contacts (the same system used in the rest of Bachmann's diesels of that era). Like the first version, couplers are truck-mounted Rapidos and all gearing is plastic. Performance is much improved over the original version, running quite smoothly and relatively quietly (no problems derailing either). The paint on the second version is a bit fancier as well - with richer (and probably more accurate) colors, along with a correctly painted nose and a silver-painted exhaust stack.
The real problem with both of these early models is their truck gears. The white plastic (nylon) that Bachmann used for their diesel gears back in the 80s and 90s was pretty cruddy. Consequently, it is becoming increasingly difficult to find any of these early DD40's with their gears intact. The gears that the axles mount to are particularly susceptible to cracking. And given the age of these models (and despite their supposed "Lifetime" warranty), Bachmann no longer services this problem. As of this writing, Bachmann is only offering SD45 or Dash 8-40C's as warranty replacements for old DD40's (this despite the fact that they now have the new DCC-equipped DD40 available as a potential replacement). OK, so how about fixing your old DD yourself? Well, NWSL offered the below listed replacement gears once upon a time. Perhaps they still do?
#2178-6 $9.95 N DD40AX compounding gear 20T x 6.6mm OD x .160” ID, delrin
#2198-6 $14.95 ea. N DD40AX axle gears (double hubbed) 15T x 6.8mm OD x 1.65mm ID
#2199-6 $79.95 N Bachmann DD40AX geared NS 47”/72 wheelset assemblies, set (8) (full set of 8 assembled geared NS drivers)
#2200-6 $14.95 N DD40AX driver wheels only NS (plug into axle gear) (16)
Bachmann discontinued their Spectrum/Plus DD40AX circa 2004 and subsequently released a new dual-mode DCC version under their generic (non-Spectrum) "blue label" line in 2009 -
This version has a huge all-metal / split-frame chassis with dual motors (3-pole, straight-wound) and four flywheels. All 16 wheels are geared and provide pickup (no traction tires). All gearing is plastic. Directional lighting (along with the stoopid blinky LED) is controlled by an enormous PC board screwed to the top of the chassis. The decoder is mounted in a pocket in the center of the chassis underneath said PC board. It appears to be soldered to the PC board, so replacing it with something else isn't going to be an entirely straightforward operation. Room for a speaker is provided inside the plastic fuel tank, and in 2014 Bachmann actually released a DCC-Sound version with a factory-installed SoundTraxx sound decoder and speaker.
From the "huh?" department, the steps and couplers are (once again) mounted to the truck assemblies. The couplers on the first production run were Bachmann's proprietary one-piece (IE non-automatic) knuckle couplers. And from what I've been told, converting them to something else (Micro-Trains, for example) was/is a nightmare. Rapido-style couplers were also included in the box for those interested in making the switch.
Starting with the second production run, the pilots were modified to include more traditional coupler boxes (allowing for easy installation of Micro-Trains, et al couplers). The ala carte Rapidos were dropped in favor of Bachmann's E-Z Mate automatic couplers. The most recent releases come with the E-Z Mates actually installed (and once again, ala carte Rapidos in the box).
Performance on this DCC version is excellent - super smooth and super quiet in both DCC and analog mode. Pickup is flawless, slow-speed creep is sensational, and the top-end speed is quite reasonable. Pulling power is strong. And amazingly enough, this thing will operate reliably on curves as sharp as 9.75" radius (although it does tend to slow down a bit when faced with curves that sharp). The shell is muchly improved over the earlier releases as well. It's a bit shorter and much narrower (still about a scale foot wider than the prototype, though). Paint and detailing are much finer as well. Unlike the first two versions, the sidesill is a separate assembly. Another new feature is the separately applied hand-grabs on the nose. On the downside, the truck sideframes are kind of lame looking - a bit flatter and less detailed than the earlier versions. And then there's that giant blinky LED - straight out of the Lionel catalog ("whee, it's a toy"). Also, I'm told by the "prototype police" that the horns are pretty awful.
Overall though, this latest version is a fine model - and light years ahead of the earlier releases (both in looks and performance). UP modelers who aren't obsessed with 100% accuracy should be quite happy with it.
To remove the shell from either of the first two versions, spread the sides apart to free it from the four metal tabs on the chassis. It should lift up and off at that point. Same basic procedure on the DCC version, just no chassis pins to worry about.
Grades: C (for the first version), B (for the second version) and A (for the DCC versions)
First version reviewed: 8/84 Model Railroader ("Bachmann's DD40AX is manufactured in Hong Kong and features a plastic shell on a machined metal frame. The detail is sharp and the locomotive's dimensions check out well against (our) drawings. The locomotive's mechanical design is straightforward. The frame is made in two halves and held together by three screws. Plastic bushings separate the halves a bit and isolate them electrically. The trucks also feature a split frame design, and the electrical flow is directly into the frame. All 16 wheels pick up current, and there are no tiny wires to twist and turn until they eventually break. One truck is driven by a 3-pole, open-frame, double-ended motor built into the truck frame. The truck will run down the track on its own! Only the end axles of the track are driven, and one driver set has rubber traction tires. Personally, I'd like to see more powered wheels and no friction tires, but I was pleasantly surprised at how quietly and smoothly this engine ran... Wheel flange depth and profile check out closely. The back-to-back wheel gauge is about .010" tight on every wheelset... The wheels are about .010" wider than the proposed NMRA standard... I rate the locomotive's paint job good. The yellow is a bit thick and still doesn't quite cover in a place or two... The large red Union Pacific lettering breaks up over some of the side details... A nice feature is the flashing yellow beacon atop the cab. This begins flashing at a steady rate as soon as a small amount of power is applied to the track. The electronics for the beacon as well as the direction headlights are on a PC board inside the top of the shell... To my mind this is a very well-done, affordable model of a very interesting prototype, one lots of modelers will want whether they model the Union Pacific or not... Price: $35")
DCC version reviewed: 02/10 Model Railroader ("Bachmann's N scale Union Pacific DDA40X's dimensions are correct, the plastic body is nicely molded, and the paint job is sharp. Twin can motors with flywheels power all eight axles. The model has enough drawbar pull to haul a good-sized train... The mid-body gap in the shell is blocked with a black panel... Nestled in the model's split frame are two can motors. The motor-only DCC decoder rests in a notch in the center of the frame, just above the flywheels. The fuel tank is designed to accommodate a speaker. The N scale model's motors are rather noisy. It also took some tweaking of the decoder's configuration variables (CVs) to smooth out its low-speed performance. The model weighs 61/2 ounces, giving it a hefty 1.6 ounces of drawbar pull. This is enough to pull 38 freight cars on straight and level track. Because of its long wheelbase, this model performs best on 11" radius or broader curves.")